Treatment of sulfide raw materials implies direct recovery of metal therefrom or recovery of metal into a matte that is then converted for production of metal or enriched sulfide phase (e.g. copper-and-nickel converter matte produced by smelting copper-nickel raw materials) from which metals are recovered by subsequent processing. Direct recovery of metal, in particular copper, from sulfide raw materials is accomplished in a single unit or in a number of units for continuous smelting process in series. The known methods for continuous smelting have, however, until now not come to extensive commercial use. In the practice of non-ferrous extractive metallurgy, methods are primarily in use implying the recovery of metals in the form of matte, from which metals are produced by subsequent processing.
The known methods for treating sulfide raw materials to produce matte include smelting of raw materials in blast, reverberatory, electric and flash smelting furnaces.
The blast furnace smelting requires a charge containing raw material and flux, the use of a carbonaceous fuel, mainly coke, and oxygen-containing gas blowing. All the known methods for smelting sulfide raw materials in blast furnaces involve the use of carbonaceous fuel.
Depending on the compositions of the initial raw material and of the produced products, the methods for sulfide raw material treatment in blast furnaces are divided into pure pyrite smelting, partial pyrite smelting and copper-and-sulfur smelting (Orkla process).
To treat massive pyritic copper ores (i.e. ores with a low gangue content) containing at least 32% sulfur, pure pyrite smelting was used. This method involved smelting of a charge, consisting of ore with flux (quartz and limestone) additions and up to 3% wt. of coke, in a blast furnace with an open throat and with air blowing at a rate of about 1,000 to 1,200 m.sup.3 /tonne of ore. The oxygen consumption amounts to about 210 to 250 m.sup.3 /tonne of ore. During smelting, copper is recovered into matte, sulfur passes into off-gases (Smirnov V. I. Metallurgy of copper and nickel, Sverdlovsk-Moscow, Metallurgizdat, 1950, p. 176-255, and in particular p. 188, 195, 200, 252; Peters E. D. The Practice of Copper Smelting, New York, McGraw-Hill Book Company, 1911, p. 204-242, and in particular p. 236).
This method provided a high rate of desulfurization (up to 95%) and a high rate of concentration (up to 20-25:1). The concentration ratio is the relationship between the copper content in matte and the copper content in initial raw material. However, the pure pyrite smelting process was difficult to control because of an unstable heat balance and because of a long time required for the charge to pass through the furnace. Furthermore, fuel required for the process operation was expensive coke in an amount of up to 2.5-3% of the total charge weight. Some attempts were made to implement the pure pyrite smelting without coke additions, i.e. autogenously, but no positive results were attained if the process had to be conducted for a longer (several days) period (Sticht R. S. Uber das Wesen des Pyrit-Schmelzverfahrens, Halle, Wilhelm Knapp, Metallurgie, May 1906, N 9, S. 269). It should be noted that during the pure pyrite smelting process sulfur was normally lost with off-gases and had to be emitted into the atmosphere, whereby the environment was contaminated. This process was in common use at the beginning of the 20th century, but later a change over to partial pyrite smelting was done due to a gradual exhaustion of massive copper pyrite ore deposits.
The partial pyrite smelting is conducted on copper pyrite ore and/or lump-size concentrates, containing less than 32% sulfur. This method implies smelting of a charge that consists of ore and/or concentrates with flux additions and of up to 12.5% wt. carbonaceous fuel, usually coke, in a blast furnace with an open or sealed throat and an air or oxygen-enriched blowing.
The use of other carbonaceous fuels, e.g. pulverized coal, fuel oil, or natural gas, introduced through the tuyeres or the use of them in the form of combustion on products fed above the tuyeres, allows one to reduce the consumption of expensive coke to a certain extent, but does not completely eliminate its use.
The air blow rate amounts up to 1,500 m.sup.3 /tonne of sulfide raw material or even more, while the oxygen-enriched blow rate is about 775 to 1,215 m.sup.3 /tonne of sulfide material. The actual oxygen requirement for smelting one tonne of sulfide raw material, taking into account oxygen needed for coke combustion, does not exceed 150 m.sup.3. During smelting, copper is recovered into matte, sulfur transfers into off-gas (Smirnov V. I. Metallurgy of Copper and Nickel, Sverdlovsk-Moskow, Metallurgizdat, 1950, p. 199-211, and in particular p. 200 a. 252; Lebedev N. I. et al., Copper blast smelting with oxygen-enriched blowing, "Tsvetnyey metally", 1961, N 3, p. 32-39).
The partial pyrite smelting process provides a lower, as compared to the pure pyrite smelting, extent of desulfurization (up to 75%), a lower ratio of concentration (up to 4-5:1) and a low SO.sub.2 content (2 to 5%) of the off-gas, which makes it difficult to recover sulfur therefrom. Furthermore, this method involves a higher consumption of expensive and short-of-supply coke as a heat source. The use of oxygen-enriched blowing allows the cutting down of the coke requirements, but by no more than 30%.
The partial pyrite smelting process is also applied for treating copper-nickel sulfide ores and/or concentrates of pyrrhotite type providing a desulfurization rate of up to 50 to 65%. When smelting such raw material and using oxygen-enriched blowing, the coke consumption decreases, but by no more than 40%, and is maintained at about 5.8% of the charge weight (Biswas A., Davenport W. Extractive Metallurgy of Copper, Oxford, Pergamon Press, 1976, p. 100-109).
During the 1930s the so-called copper-and-sulfur process (Orkla method) was developed for smelting sulfide raw materials. This method is used to treat copper pyrite ores with a sulfur content of 40 to 45%. This process involves smelting a charge, consisting of ore and fluxes with addition of solid carbonaceous material, e.g. coke, in an amount of 10% of the total charge weight, in a blast furnace with a sealed throat. The smelting process is accomplished with air blowing at a rate of up to 1,000 m.sup.3 /tonne of ore, and the oxygen consumption herewith amounts to 210 m.sup.3 /tonne of ore. The actual oxygen requirement is even lower because some oxygen of the blow air is used for combustion of a part of the coke that plays a role of fuel in the smelting process. Another part of coke burns in the middle zone of the furnace to provide reduction of SO.sub.2 formed as a result of FeS oxidation in the bottom zone of the furnace. The products of the smelting process are matte, slag, elemental sulfur and sulfur-bearing gases, from which additional elemental sulfur is recovered in the presence of a catalyst (U.S. Pat. No. 1,860,585, Cl. 23-226, May 31, 1932).
This method provides a sufficiently high sulfur recovery in the form of elemental sulfur from sulfide materials, which is a substantial advantage in comparison to other methods. On the other hand, this method shows a low desulfurization rate (up to 85%) and a low rate of concentration (up to 5.5:1). As a result, treatment of ores, containing, for example, 2.5% copper, yields low-grade mattes, containing 8 to 10% and a maximum of 14 to 15% copper. Prior to converting, such mattes should be subjected to additional treatment in an upgrading smelting furnace (concentration smelting) and this increases the cost of raw material processing. This process also requires the use of coke, not only as a reductant for recovery of sulfur from SO.sub.2, but also as fuel. Furthermore, this process is hard to control, because it takes a long time for the charge to pass through the furnace. Sulfur-bearing gases, after a catalytic treatment, have to be discharged into the atmosphere because sulfur is difficult to recover therefrom.